H2S-resistant CeO2-NiO-MgO-Al2O3 LDH-derived catalysts for steam reforming of toluene

Recently, biomass gasification has garnered a lot of attention due to its potential to produce hydrogen-rich syngas. In this research paper, H2S resistant catalysts for steam reforming of toluene as a model tar compound is studied on CeO2-NiO-MgO-Al2O3 (Ce-NMA) hydrotalcite-derived catalysts synthesized by homogeneous urea hydrolysis. A family of Ce-NMA catalysts were synthesized with different Ce loading: 0Ce-NMA, 5Ce-NMA, 10CeNMA, 15Ce-NMA and 20Ce-NMA. Among all the catalysts, the performance of the catalysts improved up to 15CeNMA, which showed the most stable performance in the presence of H2S poison. The H2-TPR and XPS showed that the presence of ceria improved the reducibility of the catalysts by facilitating electron transfer to nickel. 15Ce-NMA gave a conversion of 82%, whereas 20Ce-NMA showed a 96% toluene conversion. However, the recovery of 15Ce-NMA was very quick (30-45min) as against that of 20Ce-NMA, which deactivated to 40% conversion and took 2 h to recover the performance. The XPS of reduced catalysts showed that Ni0/Ni2+ ratio constantly increased with increasing ceria loading due to the Ce3+/Ce4+ redox pairs, which aided the reduction of Ni2+ to Ni0. The TG/DTA analysis revealed that the highest amount of carbon was formed over 0Ce-NMA and 20Ce-NMA, meaning Ce loading was only effective till a certain amount. 15Ce-NMA demonstrated lower carbon deposition as compared to 0Ce-NMA and 20Ce-NMA. Raman analysis revealed that the type of carbon varied in the 20Ce-NMA. The graphitic carbon decreased till 15Ce-NMA but suddenly increased in 20Ce-NMA, leading to higher carbon deposition and lower activity in the catalyst.